add filemanager icon in reader menu
now we can access the filemanager in all launcher configurations
refactor out global functions showHomePage and showReaderUI
restore frontlight setting only for Kobo devices
add OPDS support
This PR implements a simple OPDS browser which can be launched
from filemanager menu.
refactoring to generic multiinputdialog
title truncation in input dialog
add return button in menu
Merge pull request #876 from chrox/opds

add OPDS support